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Is it possible to have light refract in one direction, then reflect off a mirror but come back as a straight line like the picture below?

drawing of mirror with light refracting before hitting the mirror and reflecting back in a straight line

The context of this problem is in lens optics when a microdisplay is on the frame of the glasses and light is shining into the lens to project into the eye

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  • $\begingroup$ Do you just mean that the light enters the glass from below, goes straight up, reflect off the mirror, and then go back straight down? Yes, that is just a stereotypical 1D problem and it happens, just that it is not going to contribute much in our 3D world. $\endgroup$
    – naturallyInconsistent
    May 10, 2023 at 1:09
  • $\begingroup$ Snell's law rules out that this can happen. A ray entering at an angle other than perpendicular to the surface can never become perpendicular to the surface inside the material, unless you can find a mystery material that has infinite refractive index, I guess. $\endgroup$
    – FlatterMann
    May 10, 2023 at 1:13
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    $\begingroup$ @FlatterMann Yes it possible but not in glass but rather in a magnetically biased ferrite material; at below 100GHz the gadget that does this is called a circulator, there is a whole industry specialized in making those. $\endgroup$
    – hyportnex
    May 10, 2023 at 1:17
  • $\begingroup$ @hyportnex I get your point. I would even say that we don't have to go to a circulator to get such a geometry going, but it's not really described by ray optics and Snell's law doesn't apply in that case. For a simple optical system as drawn in the OP, however, the main "problem" IMHO is that the way the entry into the material is drawn is simply not physical. There is a also a simple causality argument: how would the perpendicular ray "know" at which angle to exit? A ray optical system that "can do this" is a corner reflector, but it needs more than one reflection and it displaces the beam. $\endgroup$
    – FlatterMann
    May 10, 2023 at 1:25
  • $\begingroup$ Would this be possible with 2 refracting materials instead of 1? $\endgroup$
    – Zai1208
    May 10, 2023 at 2:09

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